#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
using namespace std;
int main()
{
	double area;
	double s;
	double a,b,c;
	cin>>a>>b>>c;
	s = (a+b+c)/2;
	area = s*(s-a)*(s-b)*(s-c);
	cout<<area<<endl;
}
